According to The Making of Star Trek, the Enterprise was built on Earth but assembled in space. According to a computer display that was created by production staff of Star Trek: Enterprise but never used on screen, Jonathan Archer was present at the launch and died the next day. This information remains non-canon, because it was never photographed on film.

In TAS: "The Counter-Clock Incident", it is stated that Sarah April's service on the Enterprise was the first time a medical officer served on a starship equipped with warp drive. However, it is established in Star Trek: Enterprise that warp-capable starships had medical personnel prior to the time of her service.

In 2265, the Enterprise was assigned to a five-year mission of deep-space exploration, and command passed to James T. Kirk. The ship's primary goal during this mission was to seek out and contact alien life. Captain Kirk's standing orders also included the investigation of all quasars and quasar-like phenomena.

Despite 2270 being given as the year Kirk's first five-year mission in command of the Enterprise came to an end (in the Star Trek: Voyager episode "Q2"), many production resources – including the booklet for the TOS Season 1 DVD set – continue to use the Star Trek Chronology's date of 2264 as the starting point of the mission. It is possible, however, that the mission ran from 2264 through 2269 and that the Enterprise did not return to Earth until 2270.

According to a line from the script of Star Trek but removed from the final draft, the crew of the Enterprise came together in a time of "ultimate crisis", much like their alternate reality counterparts did. [1]

According to a line of dialogue from the final draft script of "Mudd's Women", the Enterprise was located two years, five months, twenty-two days, and seven hours from a starbase at impulse speed in that episode.

Originally, "The Naked Time" and "Tomorrow is Yesterday" were planned to be back-to-back stories, with the events in "Tomorrow is Yesterday" happening as a result of the "cold start" of the warp drive in "The Naked Time". A change in production plans resulted in the two stories being de-linked and slightly reworked to stand alone.

The space amoeba in 2268

Some missions of discovery confronted Enterprise with entities and mechanisms that threatened great swaths of Federation and neighboring space.

The nature of its mission of exploration meant the Enterprise was frequently the only Federation military asset in a little-known, otherwise undefended frontier. When called into harm's way, the ship regularly did so with little chance of immediate support against previously unknown enemies and threats.

Happily, the Enterprise's earliest engagement of its five-year mission, against a deceptively powerful starship called the Fesarius, ended with an amicable first contact with the First Federation in 2266. Following the destruction of a colony on Cestus III, a surprise attack – from a previously unknown species – led the Enterprise to battle and pursue an evenly matched Gorn starship in 2267. (TOS: "The Corbomite Maneuver", "Arena")

The Enterprise played fox to the hounds of its four sister starships in a war game exercise on stardate 4729.4. Equipped with the new M-5computer and stripped of most of its crew, the Enterprise became a killing machine – crippling the USS Excalibur and killing its entire crew – before Kirk could re-assert control. (TOS: "The Ultimate Computer")

In 2268, the Enterprise again violated the Neutral Zone – for the purpose of espionage – and was quickly surrounded by three Romulan D7 class battle cruisers. She escaped by becoming the first Federation vessel to install and successfully utilize a (stolen) Romulan cloaking device. (TOS: "The Enterprise Incident")

In the final year of Kirk's original mission, the ship was ambushed by a trio of Romulan battle cruisers while on a routine survey. The Enterprise managed to escape through an energy field that adversely affected the ship's main computer. The malfunctioning systems were corrected by another pass through the field, this time with the Romulan ships in pursuit. The attackers then became incapacitated by the same computer malfunctions, and the Enterprise was able to escape. (TAS: "The Practical Joker")

The Enterprise's first documented refit occurred sometime between 2254 and 2265. Minor changes were made to the ship's exterior (most notably the impulse engines, warp nacelles, running lights, and hull markings). More substantial changes were made to the interior color scheme and layout of the ship.

A second, more extensive refit occurred at some point after the craft's encounter with the "galactic barrier" in 2265. This refit involved replacing the bridge module, a newer, smaller deflector dish, and refinements to the warp nacelles. The ship's interior was also upgraded. The new bridge module included consoles with triangular and circular resin buttons as well as white-colored rocker flip switches. There was another small refit sometime in early 2266, too. The white-colored rocker flip switches seen on bridge consoles and on various places on the ship were replaced with multi-colored rocker flip switches.

In the late 2260s, a new bridge module added a second turbolift, and the design moved toward a completely smooth circular configuration, both standard features on future starships. At the same time, the translucent overhead dome was obscured, not to return until the Galaxy-class bridge. (TAS: "Beyond the Farthest Star")

At the end of its five-year mission, the Enterprise returned to Earth in 2270. Following its success, the ship had become a recognized symbol of Starfleet and the Federation. Starfleet's array of unique assignment patches were abandoned for the universal adoption of the Enterprise delta symbol, previously used on the assignment patch for the USS Kelvin. (Star Trek)

The stalwart vessel itself was by then twenty-five years old and returning from a deployment that included an unprecedented number of warp-speed records, hull-pounding battles, and frame-stressing maneuvers.

The refitted Enterprise in spacedock, 2270s

System upgrades with new technologies after long deployments were far from unusual in the ship's history. However, the Enterprise's overhaul of the early 2270s became a nearly keel-up redesign and reconstruction project.

After two-and-a-half years in spacedock for refit, the Enterprise was pressed into service, weeks ahead of schedule, in response to the V'ger crisis, once again under Kirk's command.

Making contact with V'ger

Decker was temporarily demoted to commander and posted as executive officer because of his familiarity with the new design. Incomplete systems had to be serviced during the vessel's shakedown cruiseen route to V'ger, including the first test of the new warp engines.

Shortly after launch, a matter/antimatter intermix malfunction ruptured the warp field and led to the Enterprise entering into an unstable wormhole. Commander Decker belayed an order from Admiral Kirk to destroy an asteroid in their path, which had been dragged into the ruptured warp field along with them, with phasers. The refitted phasers now channeled power directly from the main engines at a point beyond the dilithium/magnatomic-initiator stage. Because of this refitted function, the intermix malfunction, and the antimatter imbalance within the warp nacelles that had resulted, caused automatic cutoff of the phasers, a design change of which Kirk had not been aware. Decker ordered the use of photon torpedoes instead; as a backup, they had been designed to draw power from a separate system in case of a major phaser loss. The timely arrival of Commander Spock brought correction to the intermix problem. (Star Trek: The Motion Picture)

Once the V'ger threat was averted, Captain Decker was listed as "missing in action" and the Enterprise remained under Admiral Kirk's command for an interim period. At some point, Kirk passed command on to Captain Spock.

Upon the Enterprise returning to Earth, Starfleet Commander in Chief Admiral Harry Morrow announced that the starship, at that point forty years old, would be decommissioned. When Morrow denied Kirk requesting permission to return to the Mutara sector, Kirk conspired with his senior officers and stole the Enterprise from Earth Spacedock, in order to recover Spock's body from the Genesis Planet – to bring it and Spock's katra, the latter possessed by Leonard McCoy, to Vulcan. As part of the plan, Kirk had Scott rig up an automation system to run the Enterprise so easily that "a chimpanzee and two trainees" could have handled the craft.

The Enterprise burning in Genesis' atmosphere

At the Enterprise's destination, the ship was attacked by a Klingon Bird-of-Prey operated by Klingon Commander Kruge, an assault that left the Enterprise disabled; Scotty's automation system was not designed for combat and overloaded when the ship was attacked. After setting the auto-destruct sequence, Kirk and his crew abandoned the ship for the surface of the Genesis Planet. Demolition charges in place in the bridge and elsewhere throughout the ship's saucer section exploded, killing a Klingon boarding party. The secondary hull (with what was left of the saucer) fell from orbit and blazingly streaked across the planet's atmosphere. (Star Trek III: The Search for Spock)

There is a difference in the appearance of the Enterprise between Star Trek II: The Wrath of Khan and Star Trek III: The Search for Spock; in Star Trek III, the ship's external appearance appeared to have deteriorated around some areas damaged by Khan's attacks (and repaired in others), while other areas of the ship that had not been damaged by Khan's attack had battle damage, including the starboard secondary hull, both nacelles, and the top of the saucer. This extra damage was explained in non-canon Star Trek literature as having occurred in spars with Klingon warships between the second and third movies. The aggressive move to attack the Enterprise was explained by the secrecy of the Genesis Planet and the overall uneasiness it created. This could also explain the Klingon aggressiveness displayed throughout the third movie. [2]

Some distinctive effects shots of the Enterprise from TOS were recreated in animation for Star Trek: The Animated Series. Depicting the ship performing any new, impressive maneuvers would have been too costly for TAS and would have taken the animators too long to show, despite frequent TAS Director Hal Sutherland later implying that a desire to portray the ship doing "barrel rolls and that kind of thing" was quite common. (Star Trek: The Magazine Volume 1, Issue 16, pp. 63 & 64)

Visual effects artist Gabriel Koerner created a re-imagined version of the pre-refit Enterprise. The design is more contemporary, while keeping the design of the original ship. A video showing the ship from various angles can be seen on YouTube. The model was also featured as the August image for the 2007 Ships of the Line calendar, as well as in the Ships of the Line coffee-table book, placed between TOS and TMP images, which included text from Michael Okuda suggesting it as one of the ideas on how to refit the ship.

Upon preparing to view the bridge of the Enterprise in the first draft script of TNG: "Relics", Montgomery Scott specified, "Show her the way she was before Stardate 5928," referencing the stardate on which TOS series finale "Turnabout Intruder" takes place. Consequently, this line of dialogue would have established that the holographic simulation of the Enterprise's bridge in "Relics" was definitely contemporaneous with the exact setting of TOS. Scott did not specify that in the final draft of the script, however. [3] The line is also not spoken on screen.

The Enterprise was to have been referenced in the first draft script of VOY: "Flashback", in connection with its near-destruction at Eminiar VII. However, all mention of the vessel was eliminated from the episode by the time the final draft of the script was written.